1. Field of the Invention
The present invention relates to a video signal block forming method for forming a video signal in blocks and for processing signals in block units.
2. Description of the Prior Art
Generally a video signal has an extremely large quantity of information, and a method of curtailing the quantity of information by high efficiency coding is employed as an effective means when recording or transmitting. One of such means is a method of dividing the image into blocks, and performing high efficiency coding in block units, and a representative coding method is an orthogonal transformation coding. Explained below is a method of dividing the video signal into blocks by referring to an example of applying the orthogonal transformation coding to components signals of the existing method.
As the sampling frequency for handling the conventional component signals,
Y :fs =13.5 MHz PA1 R-Y:fs/2 =6.75 MHz PA1 B-Y:fs/2 =6.75 MHz
are standardized. If a signal is composed of 525 vertical lines, then the number of active pixels and the number of active lines in one field are as shown in Table 1.
TABLE 1 ______________________________________ Number of active pixels Number of active lines ______________________________________ Y 720 240 R - Y 360 240 B - Y 360 240 ______________________________________
The signal sampled as shown in Table 1 is an integer multiple of 8 in both number of active pixels and number of active lines, and can be divided into blocks of 8 pixels .times.8 lines, and in this case the number of blocks is as shown in Table 2.
TABLE 2 ______________________________________ Number of horizontal blocks Number of vertical blocks ______________________________________ Y 90 30 R - Y 45 30 B - Y 45 30 ______________________________________
In such block forming method, however, the following problems are present.
The signal sampled at the above sampling frequency is an integer multiple of 8 in the number of horizontal pixels, in both luminance signal (Y) and color difference signals (R-Y, B-Y), and it was easily possible to divide into blocks composed of 8 horizontal pixels and 8 vertical pixels. However, if the number of pixels is different, for example, when the color difference signal sampled at 6.75 MHz is decimated to reduce the number of pixels in the horizontal direction in half, the number of horizontal pixels is 180, which does not agree with a multiple of 8. Therefore, when the number of active pixels in the horizontal direction is not an integer multiple of the number of horizontal pixels composing one block, conventionally, the number of active pixels in the horizontal direction was enlarged or reduced before dividing then into blocks. In other words, it was necessary to code the portion that was actually not necessary to transmit, or to code by cutting off the active pixels that should be transmitted. Besides, if the number of pixels in the vertical direction was not an integer multiple of the number of vertical pixels composing one block, a similar processing was required.